add torture test on azure

[bagder]

This is a more complete torture test than what has run on travis, as a first shot to see how much it can complete on azure.

• Introducing the "shallow" torture mode #4699 introduced "shallow" torture
• curl: fixup cleanup in error path when uploading #4705 fixed leak in curl tool upload logic
• curl: fix memory leak in OOM in etags logic #4706 fixed etags memory leak
• altsvc: make the save function ignore NULL filenames #4707 fixed segfault in alt-svc save
• Torture test memory issues #4709 addressed five separate test problems
• ntlm_wb: fix double-free in OOM #4710 double-free in OOM in the ntlm-wb code
• shallow torture tests run all through ok

[bagder]

Running through them all, even excluding the FTP ones, just takes too long time. Look at the final one before azure timed out the job:

test 0556...[send and recv HTTP]
 28450 functions to make fail

I'll land #4699 first to allow us to limit the hammering per test a bit and see if I can then tweak this to go through more tests.

[bagder]

Immediate success. First PR as a result: #4705

[bagder]

Green!

To observe: test 1456 seems to have failed (unrelated) on both azure and github recently. Area for research/marking as flaky.