Enable sccache in the default docker and CI. (#1009)

* replace ccache with sccache, pin package versions

* put ccache back temporarily to avoid breaking other CI jobs

* add sccashe_wrapper.sh script

* fix the package version syntax

* fix the pymysql package issue

* run sccache_wrapper before build if ccache server found

* set the paths before calling the sccache_wrapper

* use /tmp instead of /usr/local for cache

* try using sccache --start-server instead of wrapper

* try using redis server with sccache

* define SCCACHE_REDIS

* add redis and ping packages, and redis port

* use the new sccache redis server

* do not use sccache with staging compiler

* fix the condition syntax

* add stunnel to redis

* add tunnel verification

* separate caches for different architectures

* fix syntax for the cache tag

* quse double brackets for conditions

* add bash line to the script

* add a switch for sccache and only use it in build stage

* run check_host function when enabling sccache

* fix the invocation tags for sccache

* fix groovy syntax

* set the invocation tag in groovy

* disable sccache in clang-format stage

* try another syntax for invocation tags

* use local sccache server if can't connect to redis

* fix script syntax

* update README

* refresh readme

* readme updates

* remove the timing and verification caveat from readme

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Co-authored-by: Lisa Delaney <lisa.delaney@amd.com>

script/redis-cli.conf

@@ -0,0 +1,10 @@
+fips = no
+setuid = root
+setgid = root
+pid = /var/run/stunnel.pid
+debug = 7
+options = NO_SSLv2
+options = NO_SSLv3
+[redis-cli]
+client = yes
+accept = 127.0.0.1:6379