In as-is imports, avoid inferring comp flag and "Various Artists" altogether

# Expected result
no modification of tags with 'autotag: no' while import

# Observed result

* import behaviour 1
if comp is TRUE and albumartist is set
beet import modifies 'comp: True -> False'

* import behaviour 2
if comp is TRUE and albumartist is not set
beet import modifies 'albumartist: -> Various Artists'

Hint:
It seems that a comp with albumartist is not a comp,
but if no albumartist is set, a albumartist is set automatically which makes it indirectly with next import to a not comp.

Inconsistent behaviour.

# Version
v1.5.0

# Workaround
As workaround I call function align_album_level_fields in file beets/importer.py only if autotag is true
```python
def add(self, lib):
"""Add the items as an album to the library and remove replaced items.
"""
if config['import']['autotag'] is True:
self.align_album_level_fields()
with lib.transaction():
self.record_replaced(lib)
...
```

# Configuration (output of `beet config`) is:

```yaml
directory: ~/MusicNew
library: ~/.cache/beets/musiclibrary.db

import:
move: no
copy: yes
write: no
autotag: no
duplicate_action: ask

clutter:

plugins: inline fetchart duplicates

replace:
\.: ''
item_fields:
disc_and_track: u'%02i.%02i' % (disc, track) if disctotal > 1 else u'%02i' % (track)

paths:
default: $albumartist/$album%aunique{} ($year)/$disc_and_track $title
comp: $genre/$album%aunique{} ($year)/$track $title
singleton: Non-Album/$artist/$title
albumtype:soundtrack: Soundtracks/$album%aunique{} ($year)/$track $title
albumtype:Audiobook: Audiobook/$album%aunique{} ($year)/$track $title
fetchart:
auto: yes
cover_names: cover front back art
sources: filesystem
minwidth: 0
maxwidth: 0
quality: 0
max_filesize: 0
enforce_ratio: no
cautious: no
google_key: REDACTED
google_engine: xxx
fanarttv_key: REDACTED
lastfm_key: REDACTED
store_source: no
high_resolution: no
duplicates:
album: no
checksum: ''
copy: ''
count: no
delete: no
format: ''
full: no
keys: []
merge: no
move: ''
path: no
tiebreak: {}
strict: no
tag: ''
pathfields: {}
album_fields: {}
```