Migrate to SDK 1.3.0-dev.5.2 observatory API
* --pin-isolates is replaced by --pause_isolates_on_exit
* the observatory /unpin query is now /resume
* collect_coverage --unpin-isolates is replaced with --resume-isolates
Merge pull request #13 from cbracken/observatory-updates

Migrate to SDK 1.3.0-dev.5.2 observatory API