Make MultiJobExecutor.execute print more info on failure

[keith]

When editing this test I found that in the case MultiJobExecutor.execute fails you get this error with no extra context:

% swift test --filter testDarwinBasic
Building for debugging...
[3/3] Linking swift-driverPackageTests
Build complete! (1.25s)
Test Suite 'Selected tests' started at 2022-06-13 11:31:02.392
Test Suite 'swift-driverPackageTests.xctest' started at 2022-06-13 11:31:02.393
Test Suite 'JobExecutorTests' started at 2022-06-13 11:31:02.393
Test Case '-[SwiftDriverTests.JobExecutorTests testDarwinBasic]' started.
/Users/ksmiley/dev/oss-swift/swift-driver/Sources/SwiftDriverExecution/MultiJobExecutor.swift:310: error: -[SwiftDriverTests.JobExecutorTests testDarwinBasic] : failed: caught error: "fatalError"
Test Case '-[SwiftDriverTests.JobExecutorTests testDarwinBasic]' failed (0.492 seconds).
Test Suite 'JobExecutorTests' failed at 2022-06-13 11:31:02.885.
         Executed 1 test, with 1 failure (1 unexpected) in 0.492 (0.492) seconds
Test Suite 'swift-driverPackageTests.xctest' failed at 2022-06-13 11:31:02.885.
         Executed 1 test, with 1 failure (1 unexpected) in 0.492 (0.492) seconds
Test Suite 'Selected tests' failed at 2022-06-13 11:31:02.885.
         Executed 1 test, with 1 failure (1 unexpected) in 0.492 (0.493) seconds

We should make this output the actual info from the tools that failed