Fasten rosversion --all

[tkmtnt7000]

Faster rosversion --all.
The following is a comparison of execution times using pyinstrument.

• before (60.303s)

Program: /usr/bin/rosversion --all

60.303 main  rospkg/rosversion.py:95
└─ 60.235 get_version_from_package_name  rospkg/rosversion.py:72
   ├─ 30.819 get_path  rospkg/rospack.py:199
   │  └─ 30.819 _update_location_cache  rospkg/rospack.py:173
   │     └─ 30.811 list_by_path  rospkg/rospack.py:49
   │        ├─ 13.546 __init__  xml/etree/ElementTree.py:607
   │        │     [12 frames hidden]  xml, rospkg
   │        ├─ 10.886 walk  os.py:209
   │        │     [111 frames hidden]  os, rospkg, genericpath, stat, posixpath
   │        ├─ 3.090 [self]  
   │        └─ 2.749 find  xml/etree/ElementTree.py:694
   │              [18 frames hidden]  xml, rospkg
   └─ 29.178 get_stack_version  rospkg/rospack.py:421
      └─ 29.178 get_path  rospkg/rospack.py:199
         └─ 29.176 _update_location_cache  rospkg/rospack.py:173
            └─ 29.167 list_by_path  rospkg/rospack.py:49
               ├─ 13.520 __init__  xml/etree/ElementTree.py:607
               │     [12 frames hidden]  xml, rospkg
               ├─ 10.759 walk  os.py:209
               │     [110 frames hidden]  os, rospkg, genericpath, stat, posixpath
               ├─ 2.863 find  xml/etree/ElementTree.py:694
               │     [16 frames hidden]  xml, rospkg
               └─ 1.789 [self]  

• after (24.152s)

Program: /usr/bin/rosversion --all

24.152 main  rospkg/rosversion.py:95
└  24.047 get_version_from_package_name  rospkg/rosversion.py:72
   ├─ 12.760 get_path  rospkg/rospack.py:207
   │  └─ 12.759 _update_location_cache  rospkg/rospack.py:181
   │     └─ 12.753 list_by_path  rospkg/rospack.py:51
   │        ├─ 8.706 walk  os.py:209
   │        │     [114 frames hidden]  os, rospkg, genericpath, stat, posixpath
   │        ├─ 1.972 find  xml/etree/ElementTree.py:694
   │        │     [18 frames hidden]  xml, rospkg
   │        └─ 1.695 [self]  
   └─ 11.072 get_stack_version  rospkg/rospack.py:429
      └─ 11.069 get_path  rospkg/rospack.py:207
         └─ 11.066 _update_location_cache  rospkg/rospack.py:181
            └─ 11.065 list_by_path  rospkg/rospack.py:51
               ├─ 8.408 walk  os.py:209
               │     [106 frames hidden]  os, rospkg, genericpath, stat, posixpath
               ├─ 1.936 find  xml/etree/ElementTree.py:694
               │     [16 frames hidden]  xml, rospkg
               └─ 0.527 [self] 

cc:@iory @708yamaguchi