RFR(S) 8235629 Remove unnecessary calls to Thread::current

[Ioi Lam]

https://bugs.openjdk.java.net/browse/JDK-8235629
http://cr.openjdk.java.net/~iklam/jdk14/8235629-remove-thread-current.v01/

+ In mutex.cpp, put "assert_owner(Thread::current())" into DEBUG_ONLY to 
avoid
   the evaluation of the call in product builds.
+ Changed various "ResourceMark rm;" to "rm(THREAD)".
+ In UL logs, use "ResourceMark rm" only conditionally.

I found these locations by running "java -version" in gdb, setting a 
breakpoint
at Thread::current() and logging all the callstacks. So these are by no 
means complete,
but are rather an easy-to-fix part of JVM start-up.

Before: 0.0420053188 sec
After:  0.0417649239 sec
         99.42770374% = about .6% improvement

Thanks
- Ioi