[In Progress] cleanup perl frameworks installation scripts, see #966

Per #966, this PR is an attempt to clean up the Perl frameworks' installation scripts. Please do not merge yet.
This hard coded dependency on running the framework from `~/FrameworkBenchmarks` is all over, and it has to be removed. Luckily you have a few helpful variables for calls to `subprocess`: 
* `$FWROOT` - points to the location that the git repository was cloned into (such as `~/FrameworkBenchmarks`)
* `$IROOT` - points to the installation root. For example, `$IROOT/perl-5.18` will be the per directory
* `$TROOT` - points to the folder containing this test's source code. In this file, it would be `$FWROOT/plack`

So to fix this bit here, you need to replace `--pid-file="+home+"/FrameworkBenchmarks/plack/app.pid` with `--pid-file=$TROOT/app.pid` (and similarly for any other places in the calls to subprocess)