dhcpcd-6.8.2: do not use switch_user() in Brillo builds

Brillo builds can use minijail to change dhcpcd-6.8.2 uid and
gid, so do not use switch_user() in these builds.

BUG: 25083940
Change-Id: I175191142015298db1909ee660d2a67672a4508c
TEST: dhcpcd-6.8.2 runs as expected during weaved setup in brillo build.
1 file changed