Fix cts-tradefed script to work on MacOS

readlink does not work the same on linux and MacOs because
MacOs does not have 'realpath'. Use our own 'realpath' func
to ensure we always get the path right.

Test: ./cts-tradefed for different directories on linux and Mac
Bug: 76428311
Change-Id: I51bc246ce04dee5f0a708c68b67c27182738054c
Merged-In: I93cac42c265dcc381be2c3103dc1b033cbb66377
1 file changed