[1.9.x] Fixed #26016 -- Restored contrib.auth hashers compatibility with py-bcrypt.

      Reverted "Explicitly passed rounds as rounds to bcrypt.gensalt()"

This reverts commit 23529fb19594ffcc6ba6d716356b828157200288.

Backport of f0ad641628a3ddc4e1c208e481b9cd0e9304dc3d from master