[split] twitter-server & ostrich: Drop reflection of an MX bean

Problem:
BufferPoolMXBean was introduced in JDK 7 and for supporting JDK 6 we
needed to invoke the class loader manually and use reflection to load it
where available to provider direct byte buffer stats.  Now JDK 6 support
is dropped, no justification is left for complex piece of code.

Solution:
Remove class loading and reflection.
Import `java.lang.management.BufferPoolMXBean` interface and used it as
a Platform MX Bean.

Result:
No observable changes in exported stats.

RB_ID=521207
Merge branch 'tmp' into develop