avocado.utils.software_manager: Add local file install support to AptBackend

It turns out that apt doesn't really handle local installs
graciously as dnf/yum, but thankfully there is a program
named gdebi, shipped in Debian and Ubuntu, that would let
us do that. Use it when available (we can make gdebi a
dependency for the avocado debian package to ensure it'll
always be there).
Signed-off-by: NLucas Meneghel Rodrigues <lookkas@gmail.com>

avocado/utils/software_manager.py

@@ -663,6 +663,13 @@ class AptBackend(DpkgBackend):
         self.pm_version = ver
 
         log.debug('apt-get version: %s' % self.pm_version)
+        # gdebi-core is necessary for local installation with dependency
+        # handling
+        if not self.check_installed('gdebi-core'):
+            if not self.install('gdebi-core'):
+                log.info("SoftwareManager (AptBackend) can't install packages "
+                         "from local .deb files with dependency resolution: "
+                         "Package 'gdebi-core' could not be installed")
 
     def install(self, name):
         """
@@ -670,8 +677,11 @@ class AptBackend(DpkgBackend):
 
         :param name: Package name.
         """
-        command = 'install'
-        i_cmd = self.base_command + ' ' + command + ' ' + name
+        if os.path.isfile(name):
+            i_cmd = utils_path.find_command('gdebi') + ' -n -q ' + name
+        else:
+            command = 'install'
+            i_cmd = self.base_command + ' ' + command + ' ' + name
 
         try:
             process.system(i_cmd)