Cleanup integration tests

[Malax]

First pass at cleaning up the integration test suite. The main goal was to solve concurrency issues, but the scope expanded a bit while refactoring:

• Removes usage of app.directory, fixing concurrency issues.
• Better Java properties file handling by using java-properties gem.
• Exit codes of shell commands are now properly checked instead of silently ignored.
• Removing old code that is no longer required. This includes some rspec setup code and workarounds of former Hatchet issues.
• Remove magic strings for Java versions.
• Simplify test execution by removing many layers of indirection. Those might also have caused concurrency issues.
• Better test descriptions.
• Overall cleaner code.

There is still work to do in terms of what is tested and how - we're testing the same things as before. A proper refactoring across the JVM buildpack testing landscape is in the works.

Closes W-8239355

[schneems]

When setting keys and values one thing I like to do is make my input a hash so I can do something like this

  set_system_properties("maven.version" => version_string)

And you can also set multiple values at the same time:

set_system_properties(
  "maven.version" => version_string,
  "java.runtime.version" => "11.whatever",
)

You could implement this function like this if you desired:

def set_system_properties(set_properties = {})
  if File.file?("system.properties")
    properties = JavaProperties.load("system.properties")
  else
    properties = {}
  end

  set_properties.each do |key, value|
    properties[key.to_sym] = value
  end

  JavaProperties.write(properties, "system.properties")
end

[schneems]

From an API perspective, I feel like I want a single set_version function that does both java and maven something like:

def set_version(maven: nil, java: nil)
     set_system_properties_key("java.runtime.version", java)  if java
     set_system_properties_key("maven.version", java)  if maven
end