REGTEST: ssl: test the "set ssl cert" CLI command

Add a reg-test which test the update of a certificate over the CLI. This
test requires socat and curl.

This commit also adds an ECDSA certificate in the ssl directory.
diff --git a/reg-tests/ssl/ecdsa.pem b/reg-tests/ssl/ecdsa.pem
new file mode 100644
index 0000000..e737689
--- /dev/null
+++ b/reg-tests/ssl/ecdsa.pem
@@ -0,0 +1,17 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----
+-----BEGIN PRIVATE KEY-----
+MIG2AgEAMBAGByqGSM49AgEGBSuBBAAiBIGeMIGbAgEBBDDZMkuztqaUgCAC9/7P
+CsmlC2ac7rWerq5+NKbP0Cz1+mao6+F5Hc8DKNXHgi5GPr2hZANiAAQc00b9lK5L
+sJe8vTfJ79j4uladfzXyadiTGpRB0U7Y3UI7SnqRIgwevMxAhF6/f6PaDp2sp6Ew
+aMGZ5knCxsPqdjJQ7XP7Qxq1blSJMxYWY+ri/TxMMO13yw1xaCxJatM=
+-----END PRIVATE KEY-----