Mask /sys/devices/virtual/powercap by default

This mimics #5111 but without the vendor update, which is very
large on this branch.

[NO NEW TESTS NEEDED] This cannot be tested in CI as cloud
providers already don't provide these interfaces in their VMs.

Signed-off-by: Matt Heon <mheon@redhat.com>

run_linux.go

@@ -1035,6 +1035,7 @@ func setupMaskedPaths(g *generate.Generator) {
 		"/sys/firmware",
 		"/sys/fs/selinux",
 		"/sys/dev",
+		"/sys/devices/virtual/powercap",
 	} {
 		g.AddLinuxMaskedPaths(mp)
 	}