tests: include stdout of failed commands in JUnit

All of the shell commands used by `make test-cmd` log success and
failures to stdout, e.g.:
   get.sh -> if_has_string ->
   2c9153576e/hack/lib/test.sh (L340-L360)

juLog captured stdout in addition to forwarding it to the overall test stdout,
but then only used it to check for text that indicates a problem. The result
was that after a test failure, the only thing visible in Spyglass was a fairly
useless "script error" generated by juLog for its own call chain. One had to
know that the entire build log contained more information and where to look for
it.

Now the stdout text is included in the JUnit file and thus visible when looking
at just one failed test. The output itself is still hard to read (contains one
line saying "FAIL!" and one has to know that the text below that line explains
the failure), but that is a different story.

third_party/forked/shell2junit/sh2ju.sh

@@ -20,7 +20,7 @@
 ###             -ierror="RegExp" : same as -error but case insensitive
 ###             -fail="RegExp"   : Any line from stderr which contains this pattern becomes part of
 ###                                the failure messsage, without the text matching that pattern.
-###                                Example: -failure="^ERROR: "
+###                                Example: -fail="^ERROR: "
 ###                                Default is to use the entire stderr as failure message.
 ###             -output="Path"   : path to output directory, defaults to "./results"
 ###     - Junit reports are left in the folder 'result' under the directory where the script is executed.
@@ -129,6 +129,7 @@ function juLog() {
       [[ -n "${H}" ]] && err=1
   fi
   [[ ${err} -ne 0 ]] && echo "+++ error: ${err}"         | tee -a ${outf}
+  outMsg=$(cat ${outf})
   rm -f ${outf}
 
   errMsg=$(cat ${errf})
@@ -163,6 +164,7 @@ ${failureMsg}
     <testcase assertions=\"1\" name=\"${name}\" time=\"${time}\" classname=\"${class}\">
     ${failure}
     <system-err><![CDATA[${errMsg}]]></system-err>
+    <system-out><![CDATA[${outMsg}]]></system-out>
     </testcase>
   "
   ## testsuite block