Move qmake plugin to bst-plugins-experimental
Continuing moving plugins from BuildStream to bst-plugins-experimental.
See !18 (merged) !19 (merged) !20 (merged) !23 (merged) !24 (merged)
Continuing moving plugins from BuildStream to bst-plugins-experimental.
See !18 (merged) !19 (merged) !20 (merged) !23 (merged) !24 (merged)