software_manager: Removing unused imports

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
software_manager: Fix docstring

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
software_manager: Remove unused variables

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
software_manager: Fix used of reserved keyword file

Since all sm users in the code call the method using
positional params, this change should be harmless,
and we get rid of one source of pylint complaints.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
software_manager: Use a more python idiomatic way to choose backend

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
software_manager: Replace catch all exceptions with specific exceptions

Yay for one more bad practice going away from this code...

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
software_manager: Yum - Handle exceptions when finding package providers

Some times, we may get SSL certificate errors when asking
yum to find which package provides a given file. As the
purpose of software_manager is usually to help the test
config process, we don't want an exception to interrupt
the entire process. Just log the exception and proceed.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
software_manager: Remove the last usage of os.system

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>