Add pid to batch's random filename

Batch's `%RANDOM%` resolution is limited to about a second, so if you are
calling hab multiple times at once you will end up with more than one hab
process using the same temp files and causing errors when the first one
to finish cleans up after itself.

Add the pid to the dirname to address this.

bin/hab.bat

@@ -5,9 +5,22 @@
 
 @ECHO OFF
 
-:: Generate a unique temp file name
+:: Generate a unique temp folder to store hab's short term temp .bat files.
+:: Batch's %RANDOM% isn't so random, https://devblogs.microsoft.com/oldnewthing/20100617-00/?p=13673
+:: So if you are calling hab as a batch of subprocesses, you may run into issues
+:: where multiple processes use the same random folder causing the dir to get
+:: removed while the later processes finish.
+
+:: 1. To work around this issue we add the current process's PID to the filename.
+:: https://superuser.com/a/1746190
+for /f "USEBACKQ TOKENS=2 DELIMS=="  %%A in (`wmic process where ^(Name^="WMIC.exe" AND CommandLine LIKE "%%%%TIME%%%%"^) get ParentProcessId /value`) do set "PID=%%A"
+rem echo PID: %PID%
+rem timeout 10
+
+:: 2. We also add a random number to hopefully reduce the chance of name conflicts
 :uniqLoop
-set "temp_directory=%tmp%\hab~%RANDOM%"
+set "temp_directory=%tmp%\hab~%RANDOM%-%PID%"
+:: If the folder already exists, re-generate a new folder name
 if exist "%temp_directory%" goto :uniqLoop
 
 :: Create the launch and config filenames we will end up using