[SCB-350] if the file not exist, make a warn log to trace it. make th…

[jeho0815]

…e error more clearly

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[jeho0815]

Add a warn log to help the developer know the error more simple

[2018-06-05 09:41:48,247/CST][transport-vert.x-eventloop-thread-4][WARN]keyStore [server1.p12] file not exist, please check! org.apache.servicecomb.foundation.vertx.VertxTLSBuilder.buildTCPSSLOptions(VertxTLSBuilder.java:116)
[2018-06-05 09:41:48,282/CST][transport-vert.x-eventloop-thread-4][ERROR] org.apache.servicecomb.transport.rest.vertx.RestServerVerticle.start(RestServerVerticle.java:78)
io.vertx.core.VertxException: io.vertx.core.VertxException: Key/certificate is mandatory for SSL
	at io.vertx.core.net.impl.SSLHelper.createContext(SSLHelper.java:305)
	at io.vertx.core.net.impl.SSLHelper.getContext(SSLHelper.java:447)
	at io.vertx.core.net.impl.SSLHelper.validate(SSLHelper.java:467)
	at io.vertx.core.http.impl.HttpServerImpl.listen(HttpServerImpl.java:258)
	at org.apache.servicecomb.transport.rest.vertx.RestServerVerticle.startListen(RestServerVerticle.java:104)
	at org.apache.servicecomb.transport.rest.vertx.RestServerVerticle.start(RestServerVerticle.java:75)
	at io.vertx.core.impl.DeploymentManager.lambda$doDeploy$10(DeploymentManager.java:481)
	at io.vertx.core.impl.ContextImpl.lambda$wrapTask$2(ContextImpl.java:344)
	at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:163)
	at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:404)
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:463)
	at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.lang.Thread.run(Thread.java:748)
Caused by: io.vertx.core.VertxException: Key/certificate is mandatory for SSL
	at io.vertx.core.net.impl.SSLHelper.createContext(SSLHelper.java:265)
	... 13 more

[coveralls]

Coverage decreased (-0.02%) to 87.477% when pulling 2b61d52 on jeho0815:Branch_master_SCB350 into 517a9ff on apache:master.