qsfp_service crashes on bad modules

[bluecmd]

If you have a broken QSFP module inserted when qsfp_service is running, it fails with:

E1008 18:30:19.830410  5199 FunctionScheduler.cpp:508] Error running the scheduled function <refreshTransceivers>: N8facebook5fboss10FbossErrorE: QSFP IDProm failed as QSFP is not ready

but otherwise continues to run. If you then restart qsfp_service it crashes with:

E1006 18:27:01.224939 28763 WedgeProductInfo.cpp:67] json parse error on line 0: expected json value
terminate called after throwing an instance of 'facebook::fboss::FbossError'
  what():  QSFP IDProm failed as QSFP is not ready
*** Aborted at 1538850421 (unix time) try "date -d @1538850421" if you are using GNU date ***
PC: @     0x7f5e3ac46fff gsignal
*** SIGABRT (@0x705b) received by PID 28763 (TID 0x7f5e439c8a80) from PID 28763; stack trace: ***
    @     0x7f5e416860c0 (unknown)
    @     0x7f5e3ac46fff gsignal
    @     0x7f5e3ac4842a abort
    @     0x7f5e3b55f0ad __gnu_cxx::__verbose_terminate_handler()
    @     0x7f5e3b55d066 (unknown)
    @     0x7f5e3b55d0b1 std::terminate()
    @     0x7f5e3b55d2c9 __cxa_throw
    @     0x562fdc2f9fa0 facebook::fboss::QsfpModule::setQsfpIdprom()
    @     0x562fdc2fc7e1 facebook::fboss::QsfpModule::updateQsfpData()
    @     0x562fdc2fbc34 facebook::fboss::QsfpModule::refreshLocked()
    @     0x562fdc2fba87 facebook::fboss::QsfpModule::refresh()
    @     0x562fdc30d81a facebook::fboss::WedgeManager::initTransceiverMap()
    @     0x562fdc2f5d77 facebook::fboss::QsfpServiceHandler::init()
    @     0x562fdc2f2ea4 main
    @     0x7f5e3ac342e1 __libc_start_main
    @     0x562fdc2f221a _start
    @                0x0 (unknown)