Added missing assertion for install and remove package
Merge pull request #30 from alquerci/add/test/install_remove_asserts

Added missing assertion for install and remove package
Added a test for the `postinstall` command
Added the `postinstall` command
Added a test that option -y, --nopostinstall is deprecated
Added a deprecation warning when the nopostinstall option is used
Added a test for the `postremove` command
Added the `postremove` command
Added a test that option -z, --nopostremove is deprecated
Added a deprecation warning when the nopostremove option is used