Allow user to define which package need to be installed before tagging.

This is for supporting tagging software collections (SC), if you have
installed meta package of SC then then name of package is different.
I.e. if you are tagging rubygem-foo package and you have ruby193-build
installed then the name of package is ruby193-rubygem-foo.
allow tagger to get values from package config and override values in global_config
merge common code from tagger and builder
Merge pull request #63 from xsuchy/pull-req-sc3

Support tagging packages from Software Collections