Don't error out if meta directory already exists
Don't error out if meta directory already exists

Summary:
The redex-generated scripts to rerun a crashing Redex run under gdb were
erroring out because of this.

Reviewed By: minjang, yuxuanchen1997

Differential Revision: D15624996

fbshipit-source-id: e0f97c9f357f56c33852d0dd2053089acc6d93c3

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex