Separate task files for different OS types

[2dvorak]

As discussed in #8, separate task files for different OS types.

For example, download_homi_tool.yml downloads homi binary and runs homi depending on whether the OS type is Linux or MacOS. Replace download_homi_tool.yml with download_homi_linux.yml, download_homi_macos.yml, and run_homi_tool.yml because only the URL for downloading homi differs from OS type while running homi is independent from the OS type. The reason for separating run_homi_tool.yml is to reduce duplicated contents.