Add minitar gem on AIX

The puppet module install command assumes tar is GNUtar, which doesn't
work on AIX. Install minitar on AIX like we do for Windows and Solaris.

Author: joshcooper

configs/projects/_shared-agent-components.rb

@@ -62,7 +62,7 @@
 proj.component 'rubygem-fast_gettext'
 proj.component 'rubygem-ffi'
 
-if platform.is_windows? || platform.is_solaris?
+if platform.is_windows? || platform.is_solaris? || platform.is_aix?
   proj.component 'rubygem-minitar'
 end