[kotlin] Error building kotlin-server with petstore yaml

Description

Error generating the kotin-sever code when using the petstore sample yaml file.

Output:

java -jar ./modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate -i ./modules/swagger-codegen/src/test/resources/2_0/petstore.yaml -l kotlin-server -o ./petstoreOut

...
[main] INFO io.swagger.codegen.AbstractGenerator - writing file /Users/somedude/projects/swagger/swagger-codegen/./petstoreOut/src/main/kotlin/io/swagger/server/models/User.kt
[main] ERROR io.swagger.codegen.AbstractGenerator - kotlin-server/api.mustache (No such file or directory)
[main] ERROR io.swagger.codegen.AbstractGenerator - can't load template kotlin-server/api.mustache
Exception in thread "main" java.lang.RuntimeException: Could not generate api file for 'Pet'
	at io.swagger.codegen.DefaultGenerator.generateApis(DefaultGenerator.java:542)
	at io.swagger.codegen.DefaultGenerator.generate(DefaultGenerator.java:749)
	at io.swagger.codegen.cmd.Generate.run(Generate.java:285)
	at io.swagger.codegen.SwaggerCodegen.main(SwaggerCodegen.java:35)
Caused by: java.lang.RuntimeException: can't load template kotlin-server/api.mustache
	at io.swagger.codegen.AbstractGenerator.readTemplate(AbstractGenerator.java:51)
	at io.swagger.codegen.DefaultGenerator.processTemplateToFile(DefaultGenerator.java:763)
	at io.swagger.codegen.DefaultGenerator.generateApis(DefaultGenerator.java:501)
	... 3 more

Swagger-codegen version

master as of Feb 05, 2018

Swagger declaration file content or url

./modules/swagger-codegen/src/test/resources/2_0/petstore.yaml

Command line used for generation

java -jar ./modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate -i ./modules/swagger-codegen/src/test/resources/2_0/petstore.yaml -l kotlin-server -o ./petstoreOut

Steps to reproduce

Run the command above against the petstore yaml

Start with the kotlin-server generation path and the missing kotlin-server/api.mustache template reported by the command. Run the petstore.yaml generation command from the issue, inspect the relevant templates and generator entry points, and consider the issue done when it generates the Pet API without the missing-template error.