Source vendorsetup.sh scripts anywhere within the repo.

When sourcing the envsetup.sh script from a deep directory
inside of the repo, the vendorsetup.sh scripts are not being
sourced. This was causing the ANDROID_ENABLE_METRICS_UPLOAD
not to be set and developer's metrics were not being uploaded.
Provided the top directory to each directory path. Also cleaned
up the function to handle whitespacing correctly.

Bug: b/169699936
Test: *Ran source ../../build/envsetup.sh from external/libchrome dir
      *Renamed repo dir to "aosp master" and source build/envsetup.sh
      *Ran the script in zsh command line interpretor
      *Ran the script in MacOS
Change-Id: I96eb73d50a1923cdda782792778b0d185a341cf9