Make DBWithTTL more like StackableDB

Summary: Now DBWithTTL takes DB* and can behave more like StackableDB. This saves us a lot of duplicate work by defining interfaces

Test Plan: ttl_test with ASAN - OK

Reviewers: emayanke

Reviewed By: emayanke

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14481
Enable regression tests to be run on other branches

Summary: When running regression tests on other branches, this will push values to entity rocksdb_build.$git_branch

Test Plan: Ran regression test on regression branch, observed values send to ODS in entity rocksdb_build.regression

Reviewers: kailiu

Reviewed By: kailiu

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14493
Print stack trace on assertion failure

Summary:
This will help me a lot! When we hit an assertion in unittest, we get the whole stack trace now.

Also, changed stack trace a bit, we now include actual demangled C++ class::function symbols!

Test Plan: Added ASSERT_TRUE(false) to a test, observed a stack trace

Reviewers: haobo, dhruba, kailiu

Reviewed By: kailiu

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14499