Changed to use sed for regex pattern matching

The code was using a mixture of shell patterns and
sed regular expression. Changed code to just used
sed regex. This will let me use more complex regex
that are needed for adding PARTUUID to uuids.

BUG=chromium:241572
TEST=./security_test_image
BRANCH=none

Change-Id: I2e8570051b31d580ae36cb82f05383a33236b88e
Reviewed-on: https://gerrit.chromium.org/gerrit/51503
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Paul Taysom <taysom@chromium.org>
Tested-by: Paul Taysom <taysom@chromium.org>

scripts/image_signing/ensure_secure_kernelparams.sh

@@ -65,6 +65,8 @@ main() {
     local testfail=0
     # A buffer to include useful information that we dump when things fail.
     local output
+    # Copy of a string before it has been through sed
+    local pre_sed
 
     if [[ $# -ne 1 ]] && [[ $# -ne 2 ]]; then
         usage
@@ -170,14 +172,11 @@ main() {
 
     # Ensure all other required regex params are present.
     for param in "${required_kparams_regex[@]}"; do
-        if [[ "$kparams_nodm" != *$param* ]]; then
+      pre_sed=" ${kparams_nodm} "
-            echo "Kernel parameters missing required value: $param"
+      kparams_nodm=$(echo "${pre_sed}" | sed "s${M} ${param} ${M} ${M}")
+      if [[ "${pre_sed}" == "${kparams_nodm}" ]]; then
+        echo "Kernel parameters missing required value: ${param}"
         testfail=1
-        else
-            # Remove matched params as we go. If all goes well, kparams_nodm
-            # will be nothing left but whitespace by the end.
-            kparams_nodm=$(echo " ${kparams_nodm} " |
-                           sed "s${M} ${param} ${M} ${M}")
       fi
     done