Bug 1531: Check for packages

Fixes logic to check for packages.  Originally based on dpkg -l, which could
return packages that were once installed, then removed.  Instead a new function
has been created that takes a list of packages to check and uses dpkg -L, which
will return an error if a package is not, or no longer, installed

Fixes bug 1531

Change-Id: Id096cf969aacca62dc7783b803e7925c796e325d
Signed-off-by: beierlm <mark.beierl@canonical.com>