876725 - adding support for best effort install of content and unit tests

https://bugzilla.redhat.com/show_bug.cgi?id=876725

I would like some feedback about client output as well. The bug report mentions possible use of a flag to enforce best effort install, but I think this should be a default behavior. API as well as client output is updated to return errors in the installation if any in this case, so I can't think of a particular use case where user will not want to install packages that can be installed.  


$ pulp-admin rpm consumer package install run --consumer-id test-consumer -n pulp-test-package -n pulp-dot-2.0-test -n fail-pkg1 -n fail-pkg2
Install task created with id [106f4674-b3f6-44f4-b4be-0d1ef33cccfb]

This command may be exited via ctrl+c without affecting the install.

Refresh Repository Metadata             [ OK ]
Downloading Packages                    [ OK ]
Check Package Signatures                [ OK ]
Running Test Transaction                [ OK ]
Running Transaction                     [ OK ]
Install Completed

+----------------------------------------------------------------------+
                               Installed
+----------------------------------------------------------------------+

Name:    pulp-test-package
Version: 0.3.1
Arch:    x86_64
Repoid:  test-repo

Name:    pulp-dot-2.0-test
Version: 0.1.2
Arch:    x86_64
Repoid:  test-repo


Failed to install following packages:

fail-pkg2 : No package(s) available to install

fail-pkg1 : No package(s) available to install