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>
231befab51