Fix memory leak in hash_table_test
Fix memory leak in hash_table_test

As reported by Valrind:

    ==45673== 27 bytes in 1 blocks are definitely lost in loss record 3 of 4
    ==45673==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
    ==45673==    by 0x5D85839: strdup (strdup.c:42)
    ==45673==    by 0x40331D: main (hash_table_test.cc:603)

Note this isn't /strictly/ speaking a leak as putenv() still owns it,
but to keep the output clean I'm fixing it.

Change-Id: I4a3ded5a0b29257443f9b5a3563e8e4f066ffba7
Reviewed-on: http://review.couchbase.org/52495
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: abhinav dangeti <d73ef2279de6577f7bf081737ee47554bbb7dc82@couchbase.com>
Reviewed-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>

couchbase/ep-engine,owendCB/ep-engine,owendCB/ep-engine,daverigby/ep-engine,daverigby/kv_engine,membase/ep-engine,hisundar/ep-engine,daverigby/ep-engine,daverigby/kv_engine,teligent-ru/ep-engine,hisundar/ep-engine,teligent-ru/ep-engine,teligent-ru/ep-engine,hisundar/ep-engine,teligent-ru/ep-engine,owendCB/ep-engine,daverigby/ep-engine,couchbase/ep-engine,membase/ep-engine,membase/ep-engine,couchbase/ep-engine,hisundar/ep-engine,daverigby/kv_engine,membase/ep-engine,owendCB/ep-engine,daverigby/kv_engine,couchbase/ep-engine,daverigby/ep-engine