This avoid conflict with os.path.isfile.

Also add must_exists parameter to check local file existance

As added to documentation [1], delete essential items from sys.modules may
cause Python to fail. Import machinery is complicated [2] and not well
documented before Python 3.3 [3] and the import system rework.

In our case, at least two issues was caused by clearing sys.modules.
- The first one impact import mechanism in our libs. If a lib import a function
(or other) with the 'from module import function' syntax, this function will be loaded,
but the module will not be properly loaded, this will result to TypeError.
For example if in our lib we use:

>>> from re import search
>>> search('(?<=-)\w+', 'spam-egg')

This will raise the following error:

  File "/usr/lib/python2.7/re.py", line 142, in search
    return _compile(pattern, flags).search(string)
TypeError: 'NoneType' object is not callable

- The second one is raised by importing a gzipped tarball in a script and store
them in 'namespace', namespace.tar for example. If we try to extract a file
from namespace.tar in subsequent scripts, we've got this error:

  File "/usr/lib/python2.7/tarfile.py", line 2112, in extractfile
    tarinfo = self.getmember(member)
  File "/usr/lib/python2.7/tarfile.py", line 1794, in getmember
    tarinfo = self._getmember(name)
  File "/usr/lib/python2.7/tarfile.py", line 2357, in _getmember
    members = self.getmembers()
  File "/usr/lib/python2.7/tarfile.py", line 1805, in getmembers
    self._load()        # all members, we first have to
  File "/usr/lib/python2.7/tarfile.py", line 2380, in _load
    tarinfo = self.next()
  File "/usr/lib/python2.7/tarfile.py", line 2319, in next
    tarinfo = self.tarinfo.fromtarfile(self)
  File "/usr/lib/python2.7/tarfile.py", line 1239, in fromtarfile
    buf = tarfile.fileobj.read(BLOCKSIZE)
  File "/usr/lib/python2.7/gzip.py", line 240, in read
    raise IOError(errno.EBADF, "read() on write-only GzipFile object")
IOError: [Errno 9] read() on write-only GzipFile object

[1] http://hg.python.org/cpython/rev/4f8160e45cb7
[2] http://python-notes.boredomandlaziness.org/en/latest/python_concepts/import_traps.html
[3] http://docs.python.org/dev/reference/import.html

Signed-off-by: Sébastien Luttringer <sebastien.luttringer@smartjog.com>

Image and version are required, so an error is raised if missing.
Description, author and is_min_version are optional, so update their default
value.

Signed-off-by: Sébastien Luttringer <sebastien.luttringer@smartjog.com>

If a chown,chmod,chgrp or utime call fail, it doesn't raise an error.
Used by extract_file_payload to have same behaviour than tar when file
is owned by root by example.

This let place clean when error occurs in building a payload when a previous
successful build have been done.

Traceback with old repository return None as uuid

- 2 new packages (image and repository).
- Split big modules into little one under packages.
- Replace full module import by needed objects
- Avoid wildcard imports
- Fix a lot of pylint error and warnings on modules

execpt if there is build directory

- Remove custom makefile
- Remove setup.py

Allow scripts to call exit() or exit(0) to interupt their execution properly.
Can save a useless brace adn tab time.

Exiting another value cause script to fail.

Database should not be exposed to external. We should use repository most of
time.

This introduce the new image format version in X.Y by upgrade from 1 to 2.0.
Where X is an image forward compatibility breaking and Y a revision.

The new format is needed because we move versionning from number to string

Reported-by: Aurélien Dunand <aurelien.dunand@smartjog.com>

Fix complex number handling in changlog introduced by 78ddf912.
Split show function in show and show_all

Add image format display
Add new options
Fix bad handling of changelog with version which are not number.

Since we use a global variable in installsystems.printer to store the arrow
level, we have to keep this module in scripts global context.

Signed-off-by: Sébastien Luttringer <sebastien.luttringer@smartjog.com>

Since the dmod and fmod setter take a string as argument and convert them to a
base 8 integer, we don't need to check and convert in integer with the
configobj validator.

Signed-off-by: Sébastien Luttringer <sebastien.luttringer@smartjog.com>

Signed-off-by: Sébastien Luttringer <sebastien.luttringer@smartjog.com>

Signed-off-by: Sébastien Luttringer <sebastien.luttringer@smartjog.com>

Signed-off-by: Sébastien Luttringer <sebastien.luttringer@smartjog.com>