More logging and be failfast around mtaYamlFile

- don't log a message and continue when it is clear that we cannot succeed
    together with error raised later during attempt not parse a non-existing
    file
  - More log output in order to clarify what happens with mta.yaml

test/groovy/MtaBuildTest.groovy

@@ -40,7 +40,7 @@ public class MtaBuildTest extends BasePiperTest {
     @Before
     void init() {
 
-        helper.registerAllowedMethod('fileExists', [String], { s -> false })
+        helper.registerAllowedMethod('fileExists', [String], { s -> s == 'mta.yaml' })
         helper.registerAllowedMethod('sh', [Map], { Map m -> getVersionWithoutEnvVars(m) })
 
         binding.setVariable('PATH', '/usr/bin')
@@ -90,9 +90,10 @@ public class MtaBuildTest extends BasePiperTest {
 
     @Test
     void noMtaPresentTest() {
-
-        jryr.registerYaml('mta.yaml', { throw new FileNotFoundException() })
-        thrown.expect(FileNotFoundException)
+        helper.registerAllowedMethod('fileExists', [String], { false })
+        thrown.expect(AbortException)
+        thrown.expectMessage('\'mta.yaml\' not found in project sources and \'applicationName\' not provided as parameter ' +
+                                '- cannot generate \'mta.yaml\' file.')
 
         jsr.step.mtaBuild(script: nullScript, buildTarget: 'NEO')
     }

vars/mtaBuild.groovy

@@ -51,11 +51,14 @@ void call(Map parameters = [:]) {
 
             if (!fileExists(mtaYamlName)) {
                 if (!applicationName) {
-                    echo "'applicationName' not provided as parameter - will not try to generate ${mtaYamlName} file"
+                    error "'${mtaYamlName}' not found in project sources and 'applicationName' not provided as parameter - cannot generate '${mtaYamlName}' file."
                 } else {
+                    echo "[INFO] '${mtaYamlName}' file not found in project sources, but application name provided as parameter - generating '${mtaYamlName}' file."
                     MtaUtils mtaUtils = new MtaUtils(this)
                     mtaUtils.generateMtaDescriptorFromPackageJson("package.json", mtaYamlName, applicationName)
                 }
+            } else {
+                echo "[INFO] '${mtaYamlName}' file found in project sources."
             }
 
             def mtaYaml = readYaml file: mtaYamlName