The other test root tier1 groups are named tier1, renaming the hotspot_tier1 test group makes it consistent among the groups. It also enables the use of run-test to run all of the Tier1 tests:

make run-test-tier1
Building target 'run-test-tier1' in configuration 'macosx-x64'
warning: no debug symbols in executable (-arch x86_64)
warning: no debug symbols in executable (-arch x86_64)
Test selection 'tier1', will run:
* jtreg:open/test/hotspot/jtreg:tier1
* jtreg:open/test/jdk:tier1
* jtreg:open/test/langtools:tier1
* jtreg:open/test/nashorn:tier1
* jtreg:open/test/jaxp:tier1