The trick turned out to be to set the jvm args for the keystore on the
JMeter tag. Then everything worked fine :
<jmeter forceBuildFailure="true"
jmeterhome="${jmeter.install.dir}"
testplan="${jmeter.testplan}"
resultlog="${jmeter.result.file}">
<property
name="jmeter.save.saveservice.output_format" valu
e="xml"/>
<jvmarg value="-Djavax.net.ssl.keyStore=.keystore"/>
<jvmarg
value="-Djavax.net.ssl.keyStorePassword=hello"/>
</jmeter>