bp:Create install/bin earlier

Create the install/bin directory before it is used
the first time.

Prior to this change it made the buildbot fail [1].

[1] http://factory.couchbase.com/view/commit_validation/view/couchdb/job/couchdb-gerrit-views-pre-merge-master/71/console

Change-Id: Idfe33f37fab84f68954a4e48788b5f4595330848
Orig-Change-Id: If9b7ede8ea86d2d9307899b8a203a91d2c04552d
Reviewed-on: http://review.couchbase.org/30843
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>