Abstract 'rm' shell command in guestagent

Fix proposed to branch: master
Review: https://review.openstack.org/170642

Reviewed: https://review.openstack.org/170642
Committed: https://git.openstack.org/cgit/openstack/trove/commit/?id=2eb05f8897bb17def1573380da0a05942c42cf29
Submitter: Jenkins
Branch: master

commit 2eb05f8897bb17def1573380da0a05942c42cf29
Author: Petr Malik <email address hidden>
Date: Thu Apr 2 15:23:57 2015 -0400

    Abstract rm/chmod shell commands in guestagent

    The guestagent commonly executes basic shell commands
    across multiple files and datastores.
    Each datastore currently scripts its own shell calls.
    Apart from cluttering the Python code with shell constructs,
    it also makes maintenance of the shell calls more difficult by
    requiring the same change be made across multiple lines,
    source files and/or potentially even datastores.

    The goal of this patch set is to provide a simple straightforward
    interface for most common shell calls used across the guestagent
    code while encapsulating the related shell code into a single module.

    This patch set includes refactoring of 'rm' and 'chmod' calls.
    It also introduces unit tests ('guestagent/test_operating_system')
    for the above implementations.

    The shell code was moved into 'common/operating_system' module.
    The replacing interface is:

    def remove(path, force=False, recursive=True, **kwargs):
        """Remove a given file or directory.

    def chmod(path, mode, recursive=True, force=False, **kwargs):
        """Changes the mode of a given file.

    The calls also take optional keyword arguments:
        :param as_root: Execute as root.
        :type as_root: boolean

        :param timeout: Number of seconds if specified,
                                 default if not.
                                 There is no timeout if set to None.
        :type timeout: integer

    Notes on the representation of file permissions (modes):

    Generally, one can 'reset' (set modes to an exact value) or
    'add'/'remove' modes to/from the current mode.
    The above operations are represented by a new
    'operating_system.FileMode' class.
    For example, the read permission for all can be represented in the octal
    form as '444'.
    Mode on a given file can be 'reset' to this exact value
    (chmod =444 "path")
    The permissions can be added to (chmod +444 "path")
    ... or removed from the current mode (chmod -444 "path")

    The Modes constructor takes three optional lists of octal modes (flags),
    one for each of the above operations.

    "chmod u+x,g=rw,o=r" can be represented as:
    FileMode(reset=[0064], add=[0100])
    or
    FileMode(reset=[0040, 0020, 0004], add=[0100])
    or
    FileMode(reset=[0040 | 0020 | 0004], add=[0100])

    See 'operating_system.FileMode' struct for some common file modes.
    See the Python 'stat' module for more flags also accepted by the
    Python build-in functions such as 'os.chmod'.

    Change-Id: Idbfa05fdc5c48aed31989578f828a7f57aca3be2
    Closes-Bug: 1438429
    Related-Bug: 1431618
    Related-Bug: 1438430