ZET creates empty config file if enroll fails

[qrkourier]

An empty config outfile prevents subsequent attempts to enroll from succeeding. This burdens the operator or script with first noticing that the outfile exists and is empty and removing the empty outfile before re-attempting to enroll. Conditions that may cause enrollment to fail include controller unavailable and invalid OTT.

❯ /opt/openziti/bin/ziti-edge-tunnel version
v0.20.9-local

❯ /opt/openziti/bin/ziti-edge-tunnel enroll --jwt /dev/null --identity /tmp/empty.json
(721628)[        0.000]    INFO ziti_log_set_level set log level: root=3
(721628)[        0.000]    INFO ziti-sdk:ziti_enroll.c:92 ziti_enroll() Ziti C SDK version 0.30.8 @ecfee7b(HEAD) starting enrollment at (2022-11-15T23:45:17.403)
(721628)[        0.000]   ERROR ziti-sdk:jwt.c:31 parse_jwt_content() jwt input lacks a dot
(721628)[        0.000]   ERROR ziti-sdk:ziti_enroll.c:131 ziti_enroll() /github/workspace/build/_deps/ziti-sdk-c-src/library/ziti_enroll.c:110 - load_jwt(opts->jwt, ecfg, &ecfg->zejh, &ecfg->zej) => -4 (JWT has invalid format)
(721628)[        0.000]   ERROR ziti-edge-tunnel:ziti-edge-tunnel.c:2007 enroll_cb() enrollment failed: enroll failed(-4)

❯ file /tmp/empty.json
/tmp/empty.json: empty