Summary:
Added an option, --env_uri. When provided, it is used as an argument to
NewEnvFromUri(), which instantiates an Env based on it.
Test Plan:
built a simple binary that registers ChrootEnv for prefix "/", then
ran:
$ ./tmp --env_uri /tmp/ --db /abcde
/tmp/ is the chroot directory and /abcde is the db_name. Then I verified
db_bench uses /tmp/abcde
Reviewers: sdong, kradhakrishnan, lightmark
Reviewed By: lightmark
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D59325
a683d4aba9