Fix preview build tools availability check and download

src/main/groovy/com/jakewharton/sdkmanager/internal/PackageResolver.groovy

@@ -71,15 +71,20 @@ class PackageResolver {
     def buildToolsRevision = project.android.buildToolsRevision
     log.debug "Build tools version: $buildToolsRevision"
 
-    def buildToolsRevisionDir = new File(buildToolsDir, buildToolsRevision.toString())
+    def buildToolsRevisionName = buildToolsRevision.toString()
+    if (buildToolsRevisionName.contains(" rc")) {
+      // Fix folder name for preview build tools
+      buildToolsRevisionName = buildToolsRevisionName.replaceAll(" rc.*", "-preview")
+    }
+    def buildToolsRevisionDir = new File(buildToolsDir, buildToolsRevisionName)
     if (folderExists(buildToolsRevisionDir)) {
       log.debug 'Build tools found!'
       return
     }
 
     log.lifecycle "Build tools $buildToolsRevision missing. Downloading..."
 
-    def code = androidCommand.update "build-tools-$buildToolsRevision"
+    def code = androidCommand.update "build-tools-$buildToolsRevisionName"
     if (code != 0) {
       throw new StopExecutionException("Build tools download failed with code $code.")
     }