RFR (L): 8068685 - [TESTBUG] Ensure @library works in jtreg -agentvm mode

[George Triantafillou]

Please review this fix for JDK-8068685:

JBS: https://bugs.openjdk.java.net/browse/JDK-8068685
webrev: http://cr.openjdk.java.net/~gtriantafill/8068685/webrev.00 
<http://cr.openjdk.java.net/%7Egtriantafill/8068685/webrev.00>

"@build com.oracle.java.testlibrary.*" was added to all relevant tests, 
which resulted in longer test execution times.  In order to offset these 
longer test execution times and to support running jtreg in -agentvm 
mode, the following changes were made:

test/Makefile: added -agentvm option

test/testlibrary/com/oracle/java/testlibrary/ProcessTools.java: added 
-classpath since -agentvm passes the classpath differently than -othervm

*Testing shows an 11% speed improvement for JPRT execution of the 
hotspot testset, and a 48% speed improvement for 
hotspot_runtime*/gc*/compiler*/serviceability* tests.**

*Note that some tests required the explicit addition of -othervm in 
order for the tests to pass.  In addition, a number of gc, compiler and 
runtime tests were modified with @run so they would run successfully 
with -agentvm.  Consequently, reviews from members of the compiler, gc, 
runtime, and serviceability teams would be very helpful.

Thanks to Erik Helin for providing a solution for passing classpath with 
-agentvm.

The fix was tested locally on Linux with jtreg and on all platforms with 
the JPRT hotspot testset.*
*
Thanks.

-George