Revert "[#67413780] Undoing a move that travis does"

This reverts commit cfa178fde569a337c0d2dfba5ff15e55baf69717.
This change did not overwrite the default Travis behavior as
desired...reverting.
Revert "Move dropsonde-agent source files to src/ directory."

This reverts commit 928e8ec1daf22694d82eddf5acd43d3e45cc64d1.
We are thinking that cf-lamb/dropsonde-release will serve as
our Go workspace for development as well as a BOSH release
so subprojects will not have the cannonical Go project structure.
Symlink dropsonde-agent on travis.

Travis moves dropsonde-agent to a non-ideal location, try and
get around that.