bug fix: Identify update tool based on available system tools

Instead of using platform.linux_distribution() and keep a list of possible
values to match, this patch verifies the tools on the system to identify
which update tool to use in Kimchi.
So try to import yum module, apt module or run the zypper command and in
last case raise an error.

Signed-off-by: Aline Manera <alinefm@br.ibm.com>
bug fix: Identify repository management tool based on available system tools

Instead of using platform.linux_distribution() and keep a list of possible
values to match, this patch verifies the tools in the system to identify
which repository management tool to use in Kimchi.
So try to import yum module or apt_pkg module and in last case raise an error.

Signed-off-by: Aline Manera <alinefm@br.ibm.com>
Expose repo_mngt_tool to /config/capabilities

Probably, in some cases Kimchi can not be able to identify which repository
management tool to use so expose this information to properly update the
UI

Also update the API.md and test case to reflect this change

Signed-off-by: Aline Manera <alinefm@br.ibm.com>
Start up Kimchi even if no repo management tool was identified

Kimchi should not block user to use its functionalities if a repository
management tool was not identified.
So allow user starts up kimchi and raise an error only if he/she tries
to use the repository management feature.

Signed-off-by: Aline Manera <alinefm@br.ibm.com>