A temporary test to see if ivy under ng is bad

Specifically, whether or not it's causing the failures due to what
appears to be a race condition when accessing ivy.xml and report files.

Auditors: benjy
Cache bootstrap classpath calls and lock Ivy calls

This should fix the spurious failures due to concurrent ivy resolution,
which was ultimately due to not locking around ivy calls, but
exacerbated by concurrent background workers during cache checks hitting
resolution code.

Also roll back the changes in dc9d0bdeab90d9717c404f0820d514cead073efb;
nailguns were not the cause of this bug.

Auditors: benjy
Remove print statements I missed

Auditors: benjy
Temporary fix to the nailgun/ivy deadlock

Auditors: benjy
Use a reentrant lock for locking Ivy invocation

Auditors: benjy