Jemalloc-support: Added --with-jemalloc configure option

Selecting jemalloc, prevents static linking of rocksdb, as it
is dependent on tcmalloc. Default option remains tcmalloc.
Package build builds with tcmalloc support. Support for 
jemalloc in package build and perf stats/heap profiler is 
underway.

Signed-off-by: shishir gowda <shishir.gowda@sandisk.com>
Rocksdb currently has no configure option for jemalloc, because of which we can't call configure of rocksdb build with jemalloc from ceph builds.

Sure, will throw an error in the above case where --with-librocksdb-static and --with-jemalloc.