travis-ci: fine tune the use of 'set -x' in 'ci/*' scripts

The change in commit 4f2636667 (travis-ci: use 'set -x' in 'ci/*'
scripts for extra tracing output, 2017-12-12) left a couple of rough
edges:

  - 'ci/run-linux32-build.sh' is executed in a Docker container and
    therefore doesn't source 'ci/lib-travisci.sh', which would enable
    tracing executed commands.  Enable 'set -x' in this script, too.

  - 'ci/print-test-failures.sh' iterates over all the files containing
    the exit codes of all the executed test scripts.  Since there are
    over 800 such files, the loop produces way too much noise with
    tracing executed commands enabled, so disable 'set -x' for this
    script.

  - 'ci/run-windows-build.sh' busily waits in a loop for the result of
    the Windows build, producing too much noise with tracing executed
    commands enabled as well.  Disable 'set -x' for the duration of
    that loop.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ci/lib-travisci.sh

@@ -22,7 +22,9 @@ skip_branch_tip_with_tag () {
 }
 
 # Set 'exit on error' for all CI scripts to let the caller know that
-# something went wrong
+# something went wrong.
+# Set tracing executed commands, primarily setting environment variables
+# and installing dependencies.
 set -ex
 
 skip_branch_tip_with_tag

ci/print-test-failures.sh

@@ -5,6 +5,9 @@
 
 . ${0%/*}/lib-travisci.sh
 
+# Tracing executed commands would produce too much noise in the loop below.
+set +x
+
 for TEST_EXIT in t/test-results/*.exit
 do
 	if [ "$(cat "$TEST_EXIT")" != "0" ]

ci/run-linux32-build.sh

@@ -6,6 +6,8 @@
 #   run-linux32-build.sh [host-user-id]
 #
 
+set -x
+
 # Update packages to the latest available versions
 linux32 --32bit i386 sh -c '
     apt update >/dev/null &&

ci/run-windows-build.sh

@@ -69,6 +69,10 @@ esac
 
 echo "Visual Studio Team Services Build #${BUILD_ID}"
 
+# Tracing execued commands would produce too much noise in the waiting
+# loop below.
+set +x
+
 # Wait until build job finished
 STATUS=
 RESULT=
@@ -90,6 +94,7 @@ done
 # Print log
 echo ""
 echo ""
+set -x
 gfwci "action=log&buildId=$BUILD_ID" | cut -c 30-
 
 # Set exit code for TravisCI