Make WORKER_POOL_SIZE be 5 in pixel_diff and capture_skps to match the other worker scripts

Hoping that this will eliminate these kind of error messages:
********************************************************************************
	LaunchProcess: failed to execvp:
	/b/storage/chromium_builds/try-d26c23a34a9c49-6274c42b8241fb-rmistry-20170818172757-withpatch/nacl_helper
	[1:1:0818/193217.998793:ERROR:nacl_fork_delegate_linux.cc(315)] Bad NaCl helper startup ack (0 bytes)
	Maximum number of clients reachedMaximum number of clients reached
********************************************************************************


Bug: skia:6957
Change-Id: I8378f42b75d16c9f7617fae1d7c707bb9dd315da
Reviewed-on: https://skia-review.googlesource.com/36321
Reviewed-by: Ravi Mistry <rmistry@google.com>
Commit-Queue: Ravi Mistry <rmistry@google.com>
diff --git a/ct/go/worker_scripts/capture_skps/main.go b/ct/go/worker_scripts/capture_skps/main.go
index 337baf9..5988fcc 100644
--- a/ct/go/worker_scripts/capture_skps/main.go
+++ b/ct/go/worker_scripts/capture_skps/main.go
@@ -23,7 +23,7 @@
 
 const (
 	// The number of goroutines that will run in parallel to capture SKPs.
-	WORKER_POOL_SIZE = 10
+	WORKER_POOL_SIZE = 5
 )
 
 var (
diff --git a/ct/go/worker_scripts/pixel_diff/main.go b/ct/go/worker_scripts/pixel_diff/main.go
index c96f813..40af1ce 100644
--- a/ct/go/worker_scripts/pixel_diff/main.go
+++ b/ct/go/worker_scripts/pixel_diff/main.go
@@ -24,7 +24,7 @@
 
 const (
 	// The number of goroutines that will run in parallel to run pixel diff.
-	WORKER_POOL_SIZE = 10
+	WORKER_POOL_SIZE = 5
 
 	// Hacky way to detect when webpages are missing.
 	// See https://bugs.chromium.org/p/skia/issues/detail?id=6778&desc=2#c2