Fix printf escape errors in shell scripts

Fix `printf "$foo"` which treats the value of `foo` as a printf format
rather than a string.

I used the following command to find potentially problematic lines:
```
git ls-files '*.sh' | xargs egrep 'printf +("?[^"]*|[^ ]*)\$'
```
The remaining ones are false positives for this regexp.

The errors only had minor consequences: the output of `ssl-opt.sh`
contained lines like
```
Renegotiation: gnutls server strict, client-initiated .................. ./tests/ssl-opt.sh: 741: printf: %S: invalid directive
PASS
```
and in case of failure the GnuTLS command containing a substring like
`--priority=NORMAL:%SAFE_RENEGOTIATION` was not included in the log
file. With the current tests, there was no risk of a test failure
going undetected.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

tests/scripts/check-names.sh

@@ -92,7 +92,7 @@ fi
 diff macros identifiers | sed -n -e 's/< //p' > actual-macros
 
 for THING in actual-macros enum-consts; do
-    printf "Names of $THING: "
+    printf 'Names of %s: ' "$THING"
     test -r $THING
     BAD=$( grep -v '^MBEDTLS_[0-9A-Z_]*[0-9A-Z]$' $THING || true )
     if [ "x$BAD" = "x" ]; then
@@ -105,7 +105,7 @@ for THING in actual-macros enum-consts; do
 done
 
 for THING in identifiers; do
-    printf "Names of $THING: "
+    printf 'Names of %s: ' "$THING"
     test -r $THING
     BAD=$( grep -v '^mbedtls_[0-9a-z_]*[0-9a-z]$' $THING || true )
     if [ "x$BAD" = "x" ]; then