Add log level environment variable

Add a "quiet" mode for non-CI usage when we want things to be
quick and quiet.

Author: nyonson

ci/run_task.sh

@@ -5,15 +5,23 @@
 # Shellcheck can't search dynamic paths
 # shellcheck source=/dev/null
 
-set -euox pipefail
+set -euo pipefail
 
 REPO_DIR=$(git rev-parse --show-toplevel)
 
-# Make all cargo invocations verbose.
-export CARGO_TERM_VERBOSE=true
-
-# Set to false to turn off verbose output.
-flag_verbose=true
+# Make cargo invocations verbose unless in quiet mode.
+# Also control bash debug output based on log level.
+case "${MAINTAINER_TOOLS_LOG_LEVEL:-verbose}" in
+    quiet)
+        export CARGO_TERM_VERBOSE=false
+        export CARGO_TERM_QUIET=true
+        ;;
+    *)
+        export CARGO_TERM_VERBOSE=true
+        export CARGO_TERM_QUIET=false
+        set -x
+        ;;
+esac
 
 # Use the current `Cargo.lock` file without updating it.
 cargo="cargo --locked"
@@ -32,6 +40,11 @@ TASK
   - docs            Build docs with stable toolchain.
   - docsrs          Build docs with nightly toolchain.
   - bench           Run the bench tests.
+
+Environment Variables:
+  MAINTAINER_TOOLS_LOG_LEVEL    Control script and cargo output verbosity.
+    verbose (default)           Show all script and cargo messages.
+    quiet                       Suppress script messages, reduce cargo output.
 EOF
 }
 
@@ -337,9 +350,14 @@ say_err() {
 }
 
 verbose_say() {
-    if [ "$flag_verbose" = true ]; then
-        say "$1"
-    fi
+    case "${MAINTAINER_TOOLS_LOG_LEVEL:-verbose}" in
+        quiet)
+            # Suppress verbose output.
+            ;;
+        *)
+            say "$1"
+            ;;
+    esac
 }
 
 err() {