.arduino15/packages is not a directory

[SConaway]

Bug Report

On a fresh install, any command using the package manager fails.

Current behavior

# arduino-cli core update-index
Error initializing package manager: cannot initialize package manager: loading hardware packages: loading hardware from /root/.arduino15/packages: /root/.arduino15/packages is not a directory
# 

Expected behavior

# arduino-cli core update-index
Downloading missing tool builtin:ctags@5.8-arduino11...
builtin:ctags@5.8-arduino11 downloaded                                                                                                                                                                             
Installing builtin:ctags@5.8-arduino11...
builtin:ctags@5.8-arduino11 installed
Downloading missing tool builtin:serial-discovery@1.0.0...
builtin:serial-discovery@1.0.0 downloaded                                                                                                                                                                          
Installing builtin:serial-discovery@1.0.0...
builtin:serial-discovery@1.0.0 installed
Updating index: library_index.json downloaded                                                                                                                                                                      
Updating index: package_index.json downloaded
# 

Environment

• CLI version (output of arduino-cli version):

# arduino-cli version
arduino-cli Version: 0.7.0 Commit: 3809fc3

• OS and platform:

Any seems to cause this issue. I've noticed it on: 
1. Ubuntu 18.04 x64 in Docker
2. Ubuntu 19.10 x64
3. Fedora 31 x64

Additional context