Fix a few syntax issues in shell scripts

[am11]

This delta updates shell scripts for consistency. In particular, avoid mixing Bash and Unix shell syntax by replacing:

• [ $x == $y ] and [[ $x = $y ]] with [[ $x == $y ]]
• [[ $x ]] && [[ $y ]] and [ $x ] && [ $y ] with [[ $x && $y ]]
• [ ! -z $x ] and [ $x != "" ] with [ -n $x ]
• [ ! -n $x ] and [ $x == "" ] with [ -z $x ]
• ! $x == $y with $x != $y
• #!/bin/bash with #!/usr/bin/env bash
• [[ with [ in files with /bin/sh shebang

[ghost]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[ghost]

Tagging subscribers to this area: @dotnet/runtime-infrastructure
See info in area-owners.md if you want to be subscribed.

Issue Details

---

This delta updates shell scripts for consistency. In particular, avoid mixing Bash and Unix shell syntax by replacing:

• [ $x == $y ] and [[ $x = $y ]] with [[ $x == $y ]]
• [[ $x ]] && [[ $y ]] and [ $x ] && [ $y ] with [[ $x && $y ]]
• [ ! -z $x ] and [ $x != "" ] with [ -n $x ]
• [ ! -n $x ] and [ $x == "" ] with [ -z $x ]
• ! $x == $y with $x != $y
• #!/bin/bash with #!/usr/bin/env bash
• [[ with [ in files with /bin/sh shebang

Author:	am11
Assignees:	-
Labels:	area-Infrastructure
Milestone:	-

[hoyosjs]

Just a couple minor questions.

[hoyosjs]

LGTM. Thanks!

[am11]

Resolved merge conflict with 85642f8.
@hoyosjs, I don't have permissions, could you please merge this? Thanks.

[safern]

@radical could you please look at the staging failure?

[antonfirsov]

This change broke the (non-mandatory) SslStress pipeline.

When touching SslStress and HttpStress, please make sure to run the corresponding pipelines:

/azp run runtime-libraries stress-http
/azp run runtime-libraries stress-ssl