[CI] fixes #10041 move bulk of travis and appveyor logic to koch.nim (#10183)

tools/kochdocs.nim

@@ -51,6 +51,12 @@ proc execCleanPath*(cmd: string,
   if execShellCmd(cmd) != 0: quit("FAILURE", errorcode)
   putEnv("PATH", prevPath)
 
+let kochExe* = os.getAppFilename()
+  # note: assumes `kochdocs` is only used by koch.nim
+
+proc kochExec*(cmd: string) =
+  exec kochExe.quoteShell & " " & cmd
+
 proc nimexec*(cmd: string) =
   # Consider using `nimCompile` instead
   exec findNim() & " " & cmd