try the default ~/.ecryptfs/wrapped-passphrase before bailing out

  * include/ecryptfs.h, libecryptfs/key_management.c,
    utils/ecryptfs_insert_wrapped_passphrase_into_keyring.c,
    utils/ecryptfs_unwrap_passphrase.c: if the file to unwrap is
    unspecified, try to use the default ~/.ecryptfs/wrapped-passphrase
    before bailing out, LP: #359997


Signed-off-by: Dustin Kirkland <kirkland@canonical.com>