Use space-separated coverage paths.

Specify paths to instrument with coverage using space separated lists
instead of comma separated. This makes it easier to specify the lists in
a typical format in the device mk.

Test: add COVERAGE_PATHS to device-sailfish.mk, make -j60
Bug: 67998360
Change-Id: I26c67127d72bd7a153eb4a2c23eae4881a813d54