PM-980: Fix share_dir and dag2dot in pegasus-plots
PM-980: Fix share_dir and dag2dot in pegasus-plots

Several places in the code were referring to a missing variable named
'pegasus_share_dir'. These were replaced with 'share_dir'. Also, pegasus-plots
was referring to the old dag2dot instead of pegasus-graphviz.

pegasus-isi/pegasus,pegasus-isi/pegasus,pegasus-isi/pegasus,pegasus-isi/pegasus,pegasus-isi/pegasus,pegasus-isi/pegasus,pegasus-isi/pegasus,pegasus-isi/pegasus,pegasus-isi/pegasus,pegasus-isi/pegasus