When checking if mke2fs is used, compare using basename

build_image adds additional parameters (uuid, hash_seed) if
prop_dict["ext_mkuserimg"] is set to "mkuserimg_mke2fs".
The comparison does not take paths into consideration, so passing a
full path to mkuserimg_mke2fs would cause the parameters to not
be included.

This is currently not an issue for aosp builds, but could cause problems
for customized build systems.

Bug: 187742822
Test: Manual, using vendor build system, also executed 'm droid'
Change-Id: I7a8973dd0c4d8a39aea5aafcfe1aa69750fb1449