conf: fix support for private key PEM files other than PKCS#8

The Mbed TLS bug being worked around
(Mbed-TLS/mbedtls#3896)
affects _all_ PEM inputs.
`conf_set_pem` only applied the workaround to certificates and
PKCS#8 encoded keys.

`-----BEGIN PRIVATE KEY-----` is the PKCS#8 PEM header called out in
RFC 7468. While `-----BEGIN EC PRIVATE KEY-----` is not mentioned in
that RFC, RFC 5915 does describe it as a "popular format" for using
PEM encoding to store an EC key, and most crypto libraries implement it.

Origin: #27

Author: mikewadsten

common/commandline.c

@@ -303,7 +303,8 @@ void conf_set_pem(const struct storage_parse_info *info, void *raw_dest, const v
               ret < 0 ? strerror(errno) : "Short read");
     dest->iov_len = ret;
     if (strstr(dest_str, "-----BEGIN CERTIFICATE-----") ||
-        strstr(dest_str, "-----BEGIN PRIVATE KEY-----"))
+        strstr(dest_str, "-----BEGIN PRIVATE KEY-----") ||
+        strstr(dest_str, "-----BEGIN EC PRIVATE KEY-----"))
         dest->iov_len++;
     close(fd);
 }