Bug 1854019 - Add procps to custom-v8 and custom-car linux builds....

Bug 1854019 - Add procps to custom-v8 and custom-car linux builds. r=perftest-reviewers,sparky a=NPOTB

Due to some changes upstream in depot_tools, pgrep is now a required cli
tool. In particular, we fail during the fetching of the source code due
to a pgrep check if the compiler proxy is running.

Differential Revision: https://phabricator.services.mozilla.com/D188827

taskcluster/docker/custom-car-linux/Dockerfile

@@ -20,4 +20,5 @@ RUN apt-get update && \
       wget \
       zip \
       lsb-release \
-      gperf
+      gperf \
+      procps

taskcluster/docker/custom-v8/Dockerfile

@@ -18,4 +18,5 @@ RUN apt-get update && \
       tar \
       unzip \
       wget \
-      zip
+      zip \
+      procps